Search NASA⌕ Search

SEARCH · Search NASA

Results for “vortex”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 685 records · Page 38
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Vortex boundary-layer interactions

The interaction of a turbulent boundary layer (on a flat plate) with a strong artificially-generated longitudinal vortex, which may or may not actually enter the boundary layer, was studied. Experiments, including extensive hot-wire measurements, were completed for the case in which the vortex does enter the boundary layer, and measurements for the somewhat simpler cases in which the boundary layer and vortex remain distinct are now in progress. Contours of total pressure (recently acquired) and of turbulent kinetic energy at various downstream positions are presented to show the overall development of the vortex imbedded in the boundary layer.

Bradshaw, P.↗
NASA NTRS1985

VORSTAB: A computer program for calculating lateral-directional stability derivatives with vortex flow effect

A computer program based on the Quasi-Vortex-Lattice Method of Lan is presented for calculating longitudinal and lateral-directional aerodynamic characteristics of nonplanar wing-body combination. The method is based on the assumption of inviscid subsonic flow. Both attached and vortex-separated flows are treated. For the vortex-separated flow, the calculation is based on the method of suction analogy. The effect of vortex breakdown is accounted for by an empirical method. A summary of the theoretical method, program capabilities, input format, output variables and program job control set-up are described. Three test cases are presented as guides for potential users of the code.

Lan, C. Edward↗
NASA NTRS1987

Application of a panel method to wake-vortex/wing interaction and comparison with experimental data

The ability of the Vortex Separation AEROdynamics (VSAERO) program to calculate aerodynamic loads on wings due to interaction with free vortices was studied. The loads were calculated for various positions of a downstream following wing relative to an upstream vortex-generating wing. Calculated vortex-induced span loads, rolling-moment coefficients, and lift coefficients on the following wing were compared with experimental results of McMillan et al. and El-Ramly et al. Comparisons of calculated and experimental vortex tangential velocities were also made.

Smith, Brian E.↗
NASA NTRS1987

Motion and decay of vortex rings submerged in a rotational flow

The interaction between vortex rings of finite strength and an axisymmetric rotational background flow is studied by a singular perturbation method, because it is difficult to use a finite-difference method to analyze the viscous decay in the small core of a vortex ring. The analysis is carried out by combining a composite solution of a vortex ring and an unsteady Euler solution for the background rotational flow. Using the method of averaging, a numerical scheme is developed to obtain an Euler solution in which the grid and time-step sizes depend solely on the length and velocity scales of the background flow. Numerical results are presented to illustrate the interaction between the trajectories and decay rates of the vortex rings and the background rotational flow.

Ishii, K.↗
NASA NTRS1987

An Euler code calculation of blade-vortex interaction noise

An Euler code has been developed for calculation of noise radiation due to the interaction of a distributed vortex with a Joukowski airfoil. THe time-dependent incompressible flow field is first determined and then integrated to yield the resulting sound production through use of the elegant low-frequency Green's function approach. This code has several interesting numerical features involved in the vortex motion and in continuous satisfaction of the Kutta condition. In addition, it removes the limitations on Reynolds number and is much more efficient than an earlier Navier-Stokes code. Results indicate that the noise production is due to the deceleration and subsequent acceleration of the vortex as it approaches and passes the airfoil. Predicted acoustic levels and frequencies agree with measured data although a precise comparison would require the strength, size, and position of the incoming vortex to be known.

Hardin, J. C.↗
NASA NTRS1987

Numerical simulations of trailing vortex bursting

Solutions of the steady-state Navier-Stokes equations for the axisymmetric bursting of a laminar trailing vortex are computed with Newton's method and the pseudo-arc length continuation method for wide ranges of vortex strength and Reynolds number. The results indicate that a trailing vortex can undergo a transition from a state in which the core slowly diffuses to a state marked by large amplitude, spatial oscillations of core radius and core axial velocity. At the transition point the core grows rapidly in size. This event is interpreted as vortex bursting. The results also suggest that when the maximum core swirl velocity is sufficiently large the centerline axial flow downstream of transition will be reversed.

Beran, Philip S.↗
NASA NTRS1987

Investigation of the vortex flap concept on a 75-deg sweep delta wing at supersonic speeds

An experimental investigation of the aerodynamic performance of vortex flaps on a 75-deg sweep delta wing has been conducted in the NASA Langley Unitary Plan Wind Tunnel at Mach numbers from 1.7 to 2.8. The sharp leading edge vortex flaps consisted of the outboard 30 percent of the local wing semispan. Flap deflections of 0, 5, 10, and 15 deg were investigated, for both a wing-alone and a wing-body configuration. The flaps were effective in reducing the drag across the lift-coefficient range. Integration of the upper surface pressure distributions showed that the suction pressures induced by the vortex on the flap were responsible for the drag reductions. At some lift conditions, the minimum drag condition permitted hinge line separation or vortex migration inboard of the hinge line. This result is in contrast to subsonic results, where optimum conditions call for no hinge line separation. The magnitude of the drag reduction due to flap deflection generally decreased as Mach number increased. The effect of a cylindrical forebody on the drag reduction due to flap deflection was minimal.

Covell, Peter F.↗
NASA NTRS1987

A new approach to the effect of sound on vortex dynamics

Analytical results are presented on the effect of acoustic radiation on three-dimensional vortex motions in a homogeneous, slightly compressible, inviscid fluid. The flow is considered as linear and irrotational everywhere except inside a very thin cylindrical core region around the vortex filament. In the outside region, a velocity potential is introduced that must be multivalued, and it is shown how to compute this scalar potential if the motion of the vortex filament is prescribed. To find the motion of this singularity in an external potential flow, a variational principle involving a volume integral that must exclude the singular region is considered. A functional of the external potential and vortex filament position is obtained whose extrema give equations to determine the sought-after evolution. Thus, a generalization of the Biot-Savart law to flows with constant sound speed at low Mach number is obtained.

Lund, Fernando↗
NASA NTRS1987

On the onset of three-dimensionality and time-dependence in the Goertler vortex problem

The instability of large amplitude Goertler vortices in a growing boundary layer is discussed in the fully nonlinear regime. It is shown that a three-dimensional breakdown to a flow with wavy vortex boundaries similar to that which occurs in the Taylor vortex problem takes place. However, the instability is confined to the thin shear layers which have been shown to trap the region of vortex activity. The disturbance eigenfunctions decay exponentially away from the center of these layers so that the upper and lower shear layers can support independent modes of instability. The structure of the instability, in particular its location and speed of downstream propagation, is found to be entirely consistent with recent experimental results. Furthermore, it is shown that the upper and lower layers support wavy vortex instabilities with quite different frequencies. This result is again consistent with the available experimental observations.

Hall, Philip↗
NASA NTRS1986

Viscous vortex flows

Several computational studies are currently being pursued that focus on various aspects of representing the entire lifetime of the viscous trailing vortex wakes generated by an aircraft. The formulation and subsequent near-wing development of the leading-edge vortices formed by a delta wing are being calculated at modest Reynolds numbers using a three-dimensional, time-dependent Navier-Stokes code. Another computational code was developed to focus on the roll-up, trajectory, and mutual interaction of trailing vortices further downstream from the wing using a two-dimensional, time-dependent, Navier-Stokes algorithm. To investigate the effect of a cross-wind ground shear flow on the drift and decay of the far-field trailing vortices, a code was developed that employs Euler equations along with matched asymptotic solutions for the decaying vortex filaments. And finally, to simulate the conditions far down stream after the onset of the Crow instability in the vortex wake, a full three-dimensional, time-dependent Navier-Stokes code was developed to study the behavior of interacting vortex rings.

Weston, R. P.↗
NASA NTRS1987

Roles of initial condition and vortex pairing in jet noise

Sound generation by vortex pairing in circular and elliptic cold-air jets at Mach 0.15-0.35 is investigated experimentally, with a focus on the effects of initial conditions. The results are presented in graphs and interpreted using the theory of vortex sound proposed by Moehring (1978) and vortex-filament models of jet coherent structure. Tripping the nozzle boundary layer is shown to (1) preempt formation of shear-layer vortices, (2) remove the sound they produce in later pairing, and (3) increase the diffusion of coherent vorticity in the vortex rings. Hence pairing noise should not be significant in practical jets, which are initially turbulent.

Bridges, J. E.↗
NASA NTRS1988

Navier-Stokes simulations of axisymmetric vortex rings

The solution of the incompressible Navier-Stokes equations by means of a spectral method is used in the present numerical investigation of viscous axisymmetric vortex rings, in the cases of a single ring over the 0.001-1000 Re number range, and a pair of interacting rings. The propagation speeds of vortex rings of varying Re are computed and compared with the results of Saffman's (1970) theory; the present error estimate is found to be smaller than Saffman's, and to decrease with increasing Re at fixed core/ring radius ratio. The 'leapfrogging' of two vortex rings of equal sign and Re=1000 each is observed, indicating severe strain of the vortex core through the first pass and merging during the second pass.

Stanaway, S. K.↗
NASA NTRS1988

Propagation of vortex rings and starting plumes in high and low g

The propagation of vortex rings and starting plumes during crystal growth in supercooled solutions was investigated in variable gravity environment created by acceleration-deceleration routine of a NASA's KC-135 flight. A specially designed crystal growth cell was used to study convection around crystals growing in supersaturated solutions of Na2SO4 and NaCl aboard the NASA KC-135. The results of vertical velocity measurements have shown that a continuously fed plume attains a higher velocity than the individual vortex ring. The results also indicated that the vortex ring decelerates as it propagates, and slows down much more rapidly than the starting plume, indicating a less efficient transport. It is suggested that inertial effects and buoyancy effects on vortex and plume propagation can be separated in the controlled environment of a Space Station borne centrifuge.

Hallett, J.↗
NASA NTRS1988

Interaction and merging of vortex filaments

The asymptotic solutions of Navier-Stokes equations for vortex filaments of finite strength with small effective vortical cores are summarized with special emphasis placed on the physical meaning and the practical limit to the applicability of the asymptotic solution. Finite-difference solutions of Navier-Stokes equations for the marging of the filament(s) are described with a focus on the development of the approximate boundary conditions for the computational domain. An efficiency study employing a model problem is used to assess the advantages of the present approximate boundary condition method over previously used techniques. Applications of the present method are presented for the motion and decay of a 3:1 elliptic vortex ring, and for the merging process of a pair of coaxial vortex rings. A numerical procedure for the problem of local merging of vortex filaments, which requires the asymptotic analysis as well as the numerical Navier-Stokes solver, is also presented.

Liu, C. H.↗
NASA NTRS1988

Three-dimensional mean flow experimental study of 'vortex unwinding'

A seven-hole flow-angularity pressure probe was used to assess the effectiveness of vortex unwinding in a turbulent boundary layer. The vortex center moved in the spanwise and vertical direction with increasing longitudinal distance. Initially, the vortex moved rapidly; it achieved 60 percent of its total 41 mm spanwise travel before it had completed half of its travel in the longitudinal direction. The flow was studied behind the single vortex combined with the most successful unwinder. The unwinder was found to be very effective in reducing the amount of secondary flow in the boundary layer.

Mcginley, Catherine B.↗
NASA NTRS1989

An experimental investigation of the ground vortex created by a moving jet

A 1 inch circular jet moving over a fixed ground board was studied in the NASA Langley Research Center Vortex Research Center. The jet passing over the ground board at a height of three nozzle diameters creates a ground vortex which was measured by a pattern of Endevco high response pressure transducers. The results are compared to existing data to determine the effect of the ground boundary eliminated by the moving jet. The penetration of the vortex both forward of and latterly to the impact point of the jet on the ground. The resulting ground vortex penetration forward of the impact point is reduced by approximately 30 percent and the lateral penetration is reduced by 50 percent over that experienced from a stationary jet over a stationary ground board with a free stream velocity.

Stewart, V. R.↗
NASA NTRS1988

Measurements of a supersonic turbulent vortex

Mean-flow measurements of a supersonic turbulent streamwise vortex are presented. This vortex was produced by the injection of a swirling flow along the centerline of a supersonic airstream at Mach 3. Directional Mach number distributions, obtained via a five-hole flow-angularity probe, reveal vortex characteristics similar to those of the incompressible case, even though rotational Mach numbers up to 0.8 were obtained. This work is the first step of a study of the supersonic vortex breakdown phenomenon.

Metwally, O. M.↗
NASA NTRS1989

Cross-linking of two antiparallel vortex tubes

The detailed mechanisms in vortex cross-linking are unveiled by adequately resolved, direct numerical simulation of two viscous vortex tubes. There are three characteristic phases: (1) inviscid induction followed by core flattening and stretching; (2) bridging of the two vortices by accumulation of annihilated and then cross-linked vortex lines; and (3) threading of the remnants of the initial vortex pair in between the two bridges as they pull apart. These phases and the role of threading (along with bridging) in the mixing and the enstrophy cascade are explained, and it is shown that the mechanism is insensitive to asymmetries.

Melander, M. V.↗